Download Unit 1: Force and motion

Unit 1: Force and motion
Lesson 1: Types of levers
What is meant by the lever?
It is the rigid bar(straight or curved) that rotates around a
fixed point called fulcrum, and is affected by an effort
force and a resistance force
The structure of lever:
1- A Resistance force (R)
2- An effort force (F)
3- Fulcrum(O)
The importance of lever
Helping us performs heavy tasks more easily by:1- Increasing force
Some lever exerted effort by using a small force to make a
great effort as moving a heavy load
EX. Crow bar- Nutcracker - Wheel barrow - Bottle opener
2- Increasing distance
Some lever allow exerting force for a small distance to move
an object for a long distance
EX. Manual broom
3- Increasing speed
Some lever increasing the speed of objects that effect on
them EX. Hockey bat
4- Moving the force from one place to another
EX. Manual broom
5-Accuracy in performance
EX. Tweezers that used to pick up very small objects
6-Avoid dangers
EX. Coal or ice holder
That used to pick up the hot, cold and poisonous objects
Types of lever
There are three levers according to the location of
effort force, resistance and fulcrum
1- First class lever
- In this lever the fulcrum (O) is between force (F)
and resistance(R)
-First class lever is the most popular type of levers
in our daily life
-EX. Sea saw- Crow bar –Scissors-Pliers- Nail
clipper-Suction pump-Balance-Peddle-Pincer- Pliers
2- Second class lever
-In this lever resistance force (R) is between
fulcrums (O) and the effort force (F)
- EX. Wheel barrow –Nutcracker-Stapler-Bottle
opener
3- Third class lever
-In this lever the effort force (F) is between the
resistance forces (R) and fulcrum (O)
-EX. Claw hammer-Hockey bat-Manual broomIce or sweat holder-Fishing tools- Tweezers
Exercises
Lesson 1: Types of lever
1-Write the scientific term:
1- The fixed point of a rigid bar(-------------------------------)
2- Lever that have a fixed point between the force and the
resistance
(-------------------------------)
3- Lever that have the force between the resistance and
the fixed point
(-------------------------------)
4- Lever that have the resistance between the force and
the fixed point
(-------------------------------)
5- A rigid bar rotates on a fixed point, and is effected by a
force and the resistance (-------------------------------)
2- Classify the following tools according to the type
of lever:
a) Suction pump
(------------------------------)
b) Bottle opener
c) Hockey bat
d) Wheel barrow
(------------------------------)
(-------------------------------)
(-------------------------------)
3-Give reason :
1- Seesaw is a first class lever?
--------------------------------------------------------------------------------------------------------------------------------------------------2- Manual broom is a third class lever?
---------------------------------------------------------------------------------------------------------------------------------------------------
4-Compare between first, second and third class
lever ?
Unit 1: Force and motion
Lesson 2: Law of levers
The law of the levers :
The force × its arm = the resistance × its arm
(Newton) × Cm = (Newton) × (Cm)
Effort force arm:
It is the distance between the effort force and
fulcrum
Resistance arm:
It is the distance between the resistance and fulcrum
What are the lever that conserve the effort:
1First class levers
A) If the arm of the force is longer than the arm of the
resistance(The force is smaller than the resistance)
(It conserves the effort and has a mechanical benefit)
B) If the arm of the force =the arm of the resistance
(It does not conserve the effort but has a mechanical benefit)
C) If the arm of the force is shorter than the arm of the
resistance(The force is larger than the resistance)
(It does not conserve the effort and has a mechanical benefit)
2The second class levers
They conserve the effort because
Arm of the force is always longer than the arm of the resistance
(The force is smaller than the resistance)
3the third class levers
-They do not conserve the effort (but has mechanical benefit)
because
The arm of force is shorter than the arm of the resistance
(The force is larger than the resistance)
Exercises
1Complate the following sentences :
1- The law of lever states that -------------------------------2- There is a conservation of effort for the first class
lever if the ----------------- is longer than ------------------3- -----------------------Lever always converse effort while
--------------------------lever always do not converse effort
4- The force and resistance are equal in lever if ------------------------------------------------------------------------------2- write the scientific term
a) The distance between the effort force and fulcrum
(------------------------------)
b) Force × its arm = resistance × its arm
(------------------------------)
d) A type of lever that always converses effort or has a
mechanical benefit
(-------------------------------)
3-Give reason :
1-The third class levers always do not converse
effort?---------------------------------------------------------2-The force and resistance can be equal only in the
first class lever?
--------------------------------------------------------------------3-The second class levers converse effort?
----------------------------------------------------------------4- Some of the levers are important in our life
although they do not converse effort?
-----------------------------------------------------------------4-Problems
a) The length of the force arm of the first class lever is 5
cm. And the length of the arm of resistance is 15 cm. If
the resistance has a value of 300 Newton, calculate value
of the affecting force